Various voltage sources by which regenerative electric power is locally generated have the drawback that the generated electric power fluctuates strongly as it, for example, depends on weather and time of day. This particularly applies to photovoltaic generators. It makes sense to use batteries as energy buffers to cope with these fluctuations of the available electric power.
A circuitry arrangement for connecting a battery and a further voltage source to a common DC voltage link comprising a two-pole connector for the battery and a two-pole connector for the further voltage source is known from WO 2010/047422 A2. Here, a minus pole of one of the two connectors and a plus pole of the other of the two connectors are directly connected with each other, and a common choke is connected between this connection point and a connection point connecting two parallel circuits each consisting of a switch and an anti-parallel diode oriented in blocking direction. The two parallel circuits form a half-bridge between the plus pole of the one of the two connectors and the minus pole of the other of the two connectors. When the switches of the two parallel circuits are not operated but permanently held open, a battery and a further voltage source which are connected to the two connectors are connected in series with regard to each other and connected in parallel to a link capacitor of the DC voltage link. Then, the sum of their output voltages is the link voltage of the DC voltage link, and upon putting a load to the DC voltage link, the DC voltage link is recharged by the battery and the further DC voltage source according to their output voltages. By operating the switches of the parallel circuits, however, a power flow between the battery and the further DC voltage link may also be effected. This power flow may then be superimposed with the power flow from the battery and the further DC voltage source into the DC voltage link. Further, the operation of the switches allows for boosting the output voltages of the battery and the further DC voltage link present at the two two-pole connectors. In the known circuitry arrangement, a fuel cell device is provided as the further voltage source, and an inverter for operating an electric drive motor is supplied out of the DC voltage link.
A further circuitry arrangement for connecting a battery and a further voltage source to a common DC voltage link comprising a two-pole connector for the battery and a two-pole connector for the further voltage source is known from DE 10 2011 075 658 A1. This circuitry arrangement, in addition to the above details known from WO 2010/047422 A2, comprises a buffer capacitor between the two poles of each of the two two-pole connectors. This known circuitry arrangement is intended for a photovoltaic power plant in which a solar cell module and a battery are connected to the two connectors. The buffer capacitors connected in series are used as a link capacitance of the common intermediate link. An inverter connected to the common intermediate link is supplied out of the DC voltage link and feeds into an AC power grid.
David C. Hamill and Philip T. Krein: A “Zero” Ripple Technique Applicable To Any DC Converter, IEEE 1999 (Power Electronics Specialists Conference, 1999. PESC 99. 30th Annual IEEE, Volume 2, pages 1165-1171) disclose a filter for ripple currents between two two-pole connectors in which a buffer capacitor is not directly, but via a first choke, connected to one pole of a DC voltage source. This choke is magnetically coupled to a second choke which is arranged in a line leading away from this pole. The second choke may be that one of a boost converter. Such a filter may also be provided at the output end of a buck converter and include its choke and an output side capacitor. Further, a Cuk-converter with a low current ripple is disclosed. This Cuk-converter is divided into two partial circuitries which are only connected via magnetically coupled chokes. Each of these chokes is further magnetically coupled with one of the usual chokes of the Cuk-converter, and it is connected in series with a capacitor in the respective partial circuitry.
Even the two chokes of a usual Cuk-converter are often magnetically coupled; and the power flow direction between two two-pole connectors via the capacitor can be inverted, if the switching elements on both sides of its capacitor are active switching elements.
WO 2011/092774 A1 discloses a circuitry arrangement for connecting two batteries to a common DC voltage link out of which, via a motor supplier circuitry, an electro motor, particularly a switched reluctance motor/generator, is supplied. The known circuitry arrangement comprises a two-pole connector for each of the two batteries. The plus pole of one connector is connected to the plus pole of the DC voltage link via a first choke and a first parallel circuit of a switch and an anti-parallel diode oriented in blocking direction; and a minus pole of the other connector is directly connected to the minus pole of the DC voltage link. The plus pole of the one connector is further connected with the plus pole of the other connector via the first choke and a second parallel circuit of a switch and an anti-parallel diode oriented in blocking direction and a second choke connected in series with the second parallel circuit, whereas the minus pole of the other connector is connected with the minus pole of the one connector via a third parallel circuit consisting of a switch and an anti-parallel diode oriented in blocking direction. Further, the minus pole of the one connector is connected with the plus pole of the other connector via a fourth parallel circuit consisting of a switch and an anti-parallel diode oriented in blocking direction and the second choke. The first and the second chokes are magnetically coupled in such a way that a current flowing from the plus pole of the one connector through the first choke causes a magnetic flux in the same direction through a common magnetic core as an electric current from the plus pole of the other connector through the second choke.
In one embodiment of the circuitry arrangement known from WO 2011/092774 A1, two capacitors are provided instead of two batteries. In this embodiment, the first and the second chokes, between the capacitors, are connected in series with the fourth parallel circuit consisting of the switch and the anti-parallel diode oriented in blocking direction.
There still is a need of a circuitry arrangement for connecting a battery and a further voltage source, particularly a photovoltaic generator, to a common DC voltage link, in which the battery, despite its simple integration, is not subjected to high ripple currents.